Officials are probing how a 51-year-old highway bridge came to collapse in the Italian port city of Genoa yesterday, killing at least 26 people and injuring 16 others as it sent dozens of vehicles tumbling into a heap of concrete and twisted steel.

Giuliani's contradictions in Trump defence

Donald Trump's new lawyer Rudy Giuliani has made confounding and at times contradictory statements as he fights to reduce the impact on the US president of the investigation into Russian interference in the 2016 US election and hush money paid to a porn star.

The former New York City mayor has been mounting Trump's defence through the media - embracing the president's preferred approach to challenges - but it's proving to be a bewildering display.

In an interview Sunday with ABC's This Week programme Giuliani dismissed as rumour his own statements about Trump's $US130,000 payment to adult actress Stormy Daniels, said he can't speak as to whether Trump lied when he denied knowledge of the silencing agreement and wouldn't rule out the president asserting his Fifth Amendment right against self-incrimination in the Russia investigation.

Giuliani also couldn't say whether Trump's personal lawyer, Michael Cohen, had made similar payments to other women on the president's behalf.

Despite Trump's openness to sit down with special counsel Robert Mueller in the Russia investigation, Giuliani said he would strongly advise Trump against it.

"I'm going to walk him into a prosecution for perjury like Martha Stewart?" Giuliani asked, referring to the American TV personality convicted in 2004 of lying to investigators and obstruction in an insider trading case.

Giuliani couldn't guarantee that Trump wouldn't end up asserting his constitutional right to refuse to answer any questions that might incriminate him.

During a 2016 campaign rally, Trump disparaged staffers of his Democratic opponent, Hillary Clinton, for taking the Fifth amendment during a congressional investigation into Clinton's use of a private email server as secretary of state.

Giuliani also suggested that Trump wouldn't necessarily comply with a subpoena from Mueller, whose investigation Trump has repeatedly labelled a "witch hunt."

A subpoena fight would likely find its way to the Supreme Court, which has never firmly decided whether presidents can be compelled to speak under oath.

Giuliani's aggressive defence of the president in recent weeks has pleased Trump but exasperated White House aides and lawyers and supporters are questioning his tactics.

"It seems to me that the approach last week of the Trump team plays into the hands of Mueller's tactic to try, at any cost, to try to find technical violations against lower-ranking people so that they can be squeezed," Alan Dershowitz, a Harvard law professor told NBC.

Guiliani was hired by Trump last month and says he's still learning the facts of the Mueller case and the details of Trump's knowledge of the payment to Daniels, who has alleged a sexual tryst with Trump in 2006.

The $US130,000 payment was made by Cohen days before the 2016 election, raising questions of compliance with campaign finance and ethics laws.